Image coding method and device therefor

This application is a National Stage application under 35 U.S.C. § 371 of International Application No. PCT/KR2021/005837, filed on May 11, 2021, which claims the benefit of U.S. Provisional Application No. 63/023,229, filed on May 11, 2020. The disclosures of the prior applications are incorporated by reference in their entirety.

The present document relates to an image coding technique and, more particularly, to an image coding method based on intra prediction in an image coding system and a method therefor.

Nowadays, the demand for high-resolution and high-quality images/videos such as 4K, 8K or more ultra high definition (UHD) images/videos has been increasing in various fields. As the image/video data becomes higher resolution and higher quality, the transmitted information amount or bit amount increases as compared to the conventional image data. Therefore, when image data is transmitted using a medium such as a conventional wired/wireless broadband line or image/video data is stored using an existing storage medium, the transmission cost and the storage cost thereof are increased.

Further, nowadays, the interest and demand for immersive media such as virtual reality (VR), artificial reality (AR) content or hologram, or the like is increasing, and broadcasting for images/videos having image features different from those of real images, such as a game image is increasing.

Accordingly, there is a need for a highly efficient image/video compression technique for effectively compressing and transmitting or storing, and reproducing information of high resolution and high quality images/videos having various features as described above.

A technical aspect of the present disclosure is to provide a method and an apparatus for increasing image coding efficiency.

Another technical aspect of the present document is to provide an efficient intra prediction method and an apparatus therefor.

Still another technical aspect of the present document is to provide an image coding method for matrix-based intra prediction and an apparatus therefor.

Yet another technical aspect of the present document is to provide an image coding method for IPS-based intra prediction and an apparatus therefor.

According to an embodiment of the present document, there is provided an image decoding method performed by a decoding apparatus. The method may include: receiving image information comprising intra prediction type information from a bitstream, the intra prediction type information comprising an intra MIP syntax element for a first target block; deriving a value of the intra MIP syntax element; setting a variable MIP flag for a preset specific region that is the same as a region of the first target block based on the value of the intra MIP syntax element; deriving an intra prediction mode for a second target block; deriving a prediction sample for the second target block based on the intra prediction mode for the second target block; and generating a reconstructed block based on the prediction sample, wherein the intra prediction mode for the second target block may be derived based on the variable MIP flag for the first target block.

The first target block may be a left neighboring block of the second target block, the deriving of the intra prediction mode for the second target block may include: deriving a candidate intra prediction mode based on the variable MIP flag, and deriving the intra prediction mode for the second target block based on the candidate intra prediction mode, the specific region may include a sample position of (xCb−1, yCb+cbHeight−1), (xCb, yCb) may be a position of a top-left sample of the second target block, and cbHeight may indicate a height of the second target block.

The first target block may be a top neighboring block of the second target block, the deriving of the intra prediction mode for the second target block may include: deriving a candidate intra prediction mode based on the variable MIP flag; and deriving the intra prediction mode for the second target block based on the candidate intra prediction mode, the specific region may include a sample position of (xCb+cbWidth−1, yCb−1), (xCb, yCb) may be a position of a top-left sample of the second target block, and cb Width may indicate a width of the second target block.

The second target block may include a chroma block, the first target block may bea luma block related to the chroma block, and the deriving of the intra prediction mode for the second target block may include: deriving a corresponding luma intra prediction mode based on the variable MIP flag; and deriving the intra prediction mode for the second target block based on the corresponding luma intra prediction mode.

Here, the specific region may include a sample position of (xCb+cbWidth/2, yCb+cbHeight/2) based on a tree type of the second target block not being a single tree or a chroma array type thereof not being 3, (xCb, yCb) may indicate a top-left position of the chroma block in a luma sample unit, cbWidth may indicate a width of a corresponding luma block corresponding to the chroma block, and cbHeight may indicate a height of the corresponding luma block.

The variable MIP flag may be set for the specific region based on a tree type of the first target block not being a dual tree chroma.

According to another embodiment of the present document, there is provided an image encoding method performed by an encoding apparatus. The method may include: deriving a value of an intra MIP flag for a first target block when an intra MIP mode is applied to the first target block; setting a variable MIP flag for a preset specific region that is the same as a region of the first target block based on the value of the intra MIP flag; deriving an intra prediction mode for a second target block; deriving a prediction sample for the second target block based on the intra prediction mode for the second target block; deriving residual samples for the second target block based on the prediction sample; and encoding and outputting transform coefficient information generated based on the intra MIP flag and the residual samples, wherein the intra prediction mode for the second target block may be derived based on the variable MIP flag for the first target block.

According to still another embodiment of the present document, there may be provided a digital storage medium that stores image data including encoded image information and/or a bitstream generated according to an image encoding method performed by an encoding apparatus.

According to yet another embodiment of the present document, there may be provided a digital storage medium that stores image data including encoded image information and/or a bitstream to cause a decoding apparatus to perform the image decoding method.

According to the present document, it is possible to increase overall image/video compression efficiency.

According to the present document, it is possible to increase efficiency in intra prediction.

According to the present document, it is possible to increase image coding efficiency for matrix-based intra prediction.

According to the present document, it is possible to increase image coding efficiency for ISP-based intra prediction.

The effects that can be obtained through specific examples of the present disclosure are not limited to the effects listed above. For example, there may be various technical effects that a person having ordinary skill in the related art can understand or derive from the present disclosure. Accordingly, specific effects of the present disclosure are not limited to those explicitly described in the present disclosure and may include various effects that can be understood or derived from the technical features of the present disclosure.

While the present disclosure may be susceptible to various modifications and include various embodiments, specific embodiments thereof have been shown in the drawings by way of example and will now be described in detail. However, this is not intended to limit the present disclosure to the specific embodiments disclosed herein. The terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit technical idea of the present disclosure. The singular forms may include the plural forms unless the context clearly indicates otherwise. The terms such as “include” and “have” are intended to indicate that features, numbers, steps, operations, elements, components, or combinations thereof used in the following description exist, and thus should not be understood as that the possibility of existence or addition of one or more different features, numbers, steps, operations, elements, components, or combinations thereof is excluded in advance.

Meanwhile, each component on the drawings described herein is illustrated independently for convenience of description as to characteristic functions different from each other, and however, it is not meant that each component is realized by a separate hardware or software. For example, any two or more of these components may be combined to form a single component, and any single component may be divided into plural components. The embodiments in which components are combined and/or divided will belong to the scope of the patent right of the present disclosure as long as they do not depart from the essence of the present disclosure.

Hereinafter, preferred embodiments of the present disclosure will be explained in more detail while referring to the attached drawings. In addition, the same reference signs are used for the same components on the drawings, and repeated descriptions for the same components will be omitted.

This document relates to video/image coding. For example, the method/example disclosed in this document may relate to a VVC (Versatile Video Coding) standard (ITU-T Rec. H.266), a next-generation video/image coding standard after VVC, or other video coding related standards (e.g., HEVC (High Efficiency Video Coding) standard (ITU-T Rec. H.265), EVC (essential video coding) standard, AVS2 standard, etc.).

In this document, a variety of embodiments relating to video/image coding may be provided, and, unless specified to the contrary, the embodiments may be combined to each other and be performed.

In this document, a video may mean a set of a series of images over time. Generally a picture means a unit representing an image at a specific time zone, and a slice/tile is a unit constituting a part of the picture. The slice/tile may include one or more coding tree units (CTUs). One picture may be constituted by one or more slices/tiles. One picture may be constituted by one or more tile groups. One tile group may include one or more tiles.

A pixel or a pel may mean a smallest unit constituting one picture (or image). Also, ‘sample’ may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a value of a pixel, and may represent only a pixel/pixel value of a luma component or only a pixel/pixel value of a chroma component. Alternatively, the sample may refer to a pixel value in the spatial domain, or when this pixel value is converted to the frequency domain, it may refer to a transform coefficient in the frequency domain.

A unit may represent the basic unit of image processing. The unit may include at least one of a specific region and information related to the region. One unit may include one luma block and two chroma (e.g., cb, cr) blocks. The unit and a term such as a block, an area, or the like may be used in place of each other according to circumstances. In a general case, an M×N block may include a set (or an array) of samples (or sample arrays) or transform coefficients consisting of M columns and N rows.

In this document, the term “/” and “,” should be interpreted to indicate “and/or.” For instance, the expression “A/B” may mean “A and/or B.” Further, “A, B” may mean “A and/or B.” Further, “A/B/C” may mean “at least one of A, B, and/or C.” Also, “A/B/C” may mean “at least one of A, B, and/or C.”

Further, in the document, the term “or” should be interpreted to indicate “and/or.” For instance, the expression “A or B” may include 1) only A, 2) only B, and/or 3) both A and B. In other words, the term “or” in this document should be interpreted to indicate “additionally or alternatively.”

In the present disclosure, “at least one of A and B” may mean “only A”, “only B”, or “both A and B”. In addition, in the present disclosure, the expression “at least one of A or B” or “at least one of A and/or B” may be interpreted as “at least one of A and B”.

In addition, in the present disclosure, “at least one of A, B, and C” may mean “only A”, “only B”, “only C”, or “any combination of A, B, and C”. In addition, “at least one of A, B, or C” or “at least one of A, B, and/or C” may mean “at least one of A, B, and C”.

In addition, a parenthesis used in the present disclosure may mean “for example”. Specifically, when indicated as “prediction (intra prediction)”, it may mean that “intra prediction” is proposed as an example of “prediction”. That is, “prediction” in the present disclosure is not limited to “intra prediction”, and “intra prediction” may be proposed as an example of “prediction”. In addition, when indicated as “prediction (i.e., intra prediction)”, it may also mean that “intra prediction” is proposed as an example of “prediction”.

Technical features individually described in one figure in the present disclosure may be individually implemented or may be simultaneously implemented.

schematically illustrates an example of a video/image coding system to which the present disclosure is applicable.

Referring to, the video/image coding system may include a first device (source device) and a second device (receive device). The source device may deliver encoded video/image information or data in the form of a file or streaming to the receive device via a digital storage medium or network.

The source device may include a video source, an encoding apparatus, and a transmitter. The receive device may include a receiver, a decoding apparatus, and a renderer. The encoding apparatus may be called a video/image encoding apparatus, and the decoding apparatus may be called a video/image decoding apparatus. The transmitter may be included in the encoding apparatus. The receiver may be included in the decoding apparatus. The renderer may include a display, and the display may be configured as a separate device or an external component.

The video source may obtain a video/image through a process of capturing, synthesizing, or generating a video/image. The video source may include a video/image capture device and/or a video/image generating device. The video/image capture device may include, for example, one or more cameras, video/image archives including previously captured video/images, or the like. The video/image generating device may include, for example, a computer, a tablet and a smartphone, and may (electronically) generate a video/image. For example, a virtual video/image may be generated through a computer or the like. In this case, the video/image capturing process may be replaced by a process of generating related data.

The encoding apparatus may encode an input video/image. The encoding apparatus may perform a series of procedures such as prediction, transform, and quantization for compression and coding efficiency. The encoded data (encoded video/image information) may be output in the form of a bitstream.

The transmitter may transmit the encoded video/image information or data output in the form of a bitstream to the receiver of the receive device through a digital storage medium or a network in the form of a file or streaming. The digital storage medium may include various storage mediums such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. The transmitter may include an element for generating a media file through a predetermined file format, and may include an element for transmission through a broadcast/communication network. The receiver may receive/extract the bitstream and transmit the received/extracted bitstream to the decoding apparatus.

The decoding apparatus may decode a video/image by performing a series of procedures such as dequantization, inverse transform, prediction, and the like corresponding to the operation of the encoding apparatus.

The renderer may render the decoded video/image. The rendered video/image may be displayed through the display.

is a diagram schematically illustrating a configuration of a video/image encoding apparatus to which the present disclosure is applicable. Hereinafter, what is referred to as the video encoding apparatus may include an image encoding apparatus.

Referring to, the encoding apparatusmay include an image partitioner, a predictor, a residual processor, an entropy encoder, an adder, a filter, and a memory. The predictormay include an inter predictorand an intra predictor. The residual processormay include a transformer, a quantizer, a dequantizer, an inverse transformer. The residual processormay further include a subtractor. The addermay be called a reconstructor or reconstructed block generator. The image partitioner, the predictor, the residual processor, the entropy encoder, the adder, and the filter, which have been described above, may be constituted by one or more hardware components (e.g., encoder chipsets or processors) according to an embodiment. Further, the memorymay include a decoded picture buffer (DPB), and may be constituted by a digital storage medium. The hardware component may further include the memoryas an internal/external component.

The image partitionermay partition an input image (or a picture or a frame) input to the encoding apparatusinto one or more processing units. As one example, the processing unit may be called a coding unit (CU). In this case, starting with a coding tree unit (CTU) or the largest coding unit (LCU), the coding unit may be recursively partitioned according to the Quad-tree binary-tree ternary-tree (QTBTTT) structure. For example, one coding unit may be divided into a plurality of coding units of a deeper depth based on the quad-tree structure, the binary-tree structure, and/or the ternary structure. In this case, for example, the quad-tree structure may be applied first and the binary-tree structure and/or the ternary structure may be applied later. Alternatively, the binary-tree structure may be applied first. The coding procedure according to the present disclosure may be performed based on the final coding unit which is not further partitioned. In this case, the maximum coding unit may be used directly as a final coding unit based on coding efficiency according to the image characteristic. Alternatively, the coding unit may be recursively partitioned into coding units of a further deeper depth as needed, so that the coding unit of an optimal size may be used as a final coding unit. Here, the coding procedure may include procedures such as prediction, transform, and reconstruction, which will be described later. As another example, the processing unit may further include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may be split or partitioned from the above-described final coding unit. The prediction unit may be a unit of sample prediction, and the transform unit may be a unit for deriving a transform coefficient and/or a unit for deriving a residual signal from a transform coefficient.

The unit and a term such as a block, an area, or the like may be used in place of each other according to circumstances. In a general case, an M×N block may represent a set of samples or transform coefficients consisting of M columns and N rows. The sample may generally represent a pixel or a value of a pixel, and may represent only a pixel/pixel value of a luma component, or only a pixel/pixel value of a chroma component. The sample may be used as a term corresponding to a pixel or a pel of one picture (or image).

The subtractorsubtracts a prediction signal (predicted block, prediction sample array) output from the inter predictoror the intra predictorfrom an input image signal (original block, original sample array) to generate a residual signal (residual block, residual sample array), and the generated residual signal is transmitted to the transformer. In this case, as shown, a unit which subtracts the prediction signal (predicted block, prediction sample array) from the input image signal (original block, original sample array) in the encodermay be called the subtractor. The predictor may perform prediction on a processing target block (hereinafter, referred to as ‘current block’), and may generate a predicted block including prediction samples for the current block. The predictor may determine whether intra prediction or inter prediction is applied on a current block or CU basis. As discussed later in the description of each prediction mode, the predictor may generate various information relating to prediction, such as prediction mode information, and transmit the generated information to the entropy encoder. The information on the prediction may be encoded in the entropy encoderand output in the form of a bitstream.